Reference signal circuits are used to provide reference voltages or reference currents in a wide variety of integrated circuits (ICs). Within an integrated circuit, the reference voltages or currents may be used in many different circuits to provide proper reference levels for various transistor circuitry. Generally, a highly accurate and non-temperature dependent circuit, such as a band-gap voltage source, is used to generate a reference voltage or current. Such a stable reference voltage improves predictability of transistor circuitry operating with a reference voltage or current.
One integrated circuit that may operate using a reference voltage is a delta-sigma analog-to-digital converter (ADC). When a reference voltage source is coupled to the ADC, thermal noise in a reference voltage signal generated by the reference voltage source can degrade performance of the ADC. One conventional solution for reducing the thermal noise entering the ADC is the use of an external capacitor to limit noise bandwidth. FIG. 1 is a circuit illustrating an external capacitor between a reference voltage source and an ADC according to the prior art. An ADC 110 receives an analog input signal Vin at input node 102 for conversion to a digital output signal Dout at output node 104. The ADC 110 may include a pin 120 for connection of an external capacitor 122 for filtering a reference voltage signal Vref. The external capacitor 122 can be large and thus consumes extra foot print on the electronic board inside small or low-profile electronic devices, such as mobile phones. Further, the external capacitor 122 adds cost to the construction of the electronic device. Another disadvantage of the external capacitor 122 is the requirement for one or more additional pins on the chip connecting to the external capacitor 122, which increases cost and area.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for analog-to-digital converters (ADCs) employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above.